SECONDARY BATTERY INCLUDING HIGH-CAPACITY NEGATIVE ELECTRODE AND METHOD OF MANUFACTURING THE SAME

Abstract

Disclosed are a secondary battery comprising a negative electrode composed of two or more negative electrode plates and a method of manufacturing the secondary battery, wherein each of the negative electrode plates includes a lithium by-product layer formed through pre-lithiation reaction on a negative electrode current collector coated with a negative electrode active material, wherein an inorganic substance layer is formed on a negative electrode tab that is extended from an end at one side of the negative electrode current collector and is composed of an active material-non-coated portion not coated with the negative electrode active material, and negative electrode tabs of the negative electrode plates are electrically connected with one negative electrode lead to form a negative electrode terminal.

Claims

1. A secondary battery, comprising a negative electrode composed of two or more negative electrode plates, wherein each of the negative electrode plates comprises a lithium by-product layer formed through pre-lithiation reaction on a negative electrode current collector coated with a negative electrode active material, wherein an inorganic substance layer is formed on a negative electrode tab that is extended from an end at one side of the negative electrode current collector and is composed of an active material-non-coated portion not coated with the negative electrode active material, and negative electrode tabs of the negative electrode plates are electrically connected with one negative electrode lead to form a negative electrode terminal.

2. The secondary battery according to claim 1, wherein the negative electrode active material is one or more selected from the group consisting of silicon (Si), an alloy of silicon, SiB.sub.4, SiB.sub.6, Mg.sub.2Si, Ni.sub.2Si, TiSi.sub.2, MoSi.sub.2, CoSi.sub.2, NiSi.sub.2, CaSi.sub.2, CrSi.sub.2, Cu.sub.5Si, FeSi.sub.2, MnSi.sub.2, NbSi.sub.2, TaSi.sub.2, VSi.sub.2, WSi.sub.2, ZnSi.sub.2, SiC, Si.sub.3N.sub.4, Si.sub.2N.sub.2O, SiO.sub.v where 0.5≦v≦1.2, and LiSiO.

3. The secondary battery according to claim 1, wherein the negative electrode active material comprises SiO.sub.v where 0.5≦v≦1.2.

4. The secondary battery according to claim 1, wherein the lithium by-products are one or more selected from the group consisting of Li, Li.sub.2O, Li.sub.2CO.sub.3, LiCl, and LiClO.sub.4.

5. The secondary battery according to claim 1, wherein a thickness of the lithium by-product layer is 0.01 μm to 1 μm.

6. The secondary battery according to claim 1, wherein the inorganic substance is one or more selected from the group consisting of SiO.sub.2, TiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2, CeO.sub.2, MgO, CaO, ZnO, Y.sub.2O.sub.3, Pb(Zr,Ti)O.sub.3(PZT), Pb.sub.1-xLa.sub.xZr.sub.1-yTiyO.sub.3(PLZT) where 0<x<1 and 0<y<1, Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3—PbTiO.sub.3(PMN-PT), BaTiO.sub.3, hafnia(HfO.sub.2), SrTiO.sub.3, and a mixture of two or more thereof.

7. The secondary battery according to claim 1, wherein a thickness of the inorganic substance layer is 1 nm to 10 μm.

8. A method of manufacturing the secondary battery according to claim 1, the method comprising: coating a negative electrode active material on a negative electrode current collector portion, except for a portion corresponding to a negative electrode tab, of a metal sheet and then coating the negative electrode tab composed of the active material-non-coated portion that is not coated with the negative electrode active material with an inorganic substance; pre-lithiating by feeding the metal sheet manufactured through the coating into a lithium-based solvent and then applying current thereto; cutting the metal sheet manufactured through the pre-lithiating into a shape of a negative electrode plate that comprises the negative electrode current collector portion and the negative electrode tab; and forming a negative electrode terminal by stacking two or more negative electrode plates manufactured through the cutting and then electrically coupling the negative electrode tabs with a negative electrode lead.

9. The method according to claim 8, wherein, in the pre-lithiating, the lithium-based solvent is one or more selected from the group consisting of LiCl, LiBr, LiI, LiClO.sub.4, LiBF.sub.4, LiB.sub.10Cl.sub.10, LiPF.sub.6, LiCF.sub.3SO.sub.3, LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6, LiAlCl.sub.4, CH.sub.3SO.sub.3Li, CF.sub.3SO.sub.3Li, (CF.sub.3SO.sub.2).sub.2NLi, Li.sub.3N, LiI, Li.sub.5NI.sub.2, Li.sub.3N—LiI—LiOH, LiSiO.sub.4, LiSiO.sub.4—LiI—LiOH, Li.sub.2SiS.sub.3, Li.sub.4SiO.sub.4, Li.sub.4SiO.sub.4—LiI—LiOH, and Li.sub.3PO.sub.4—Li.sub.2S—SiS.sub.2.

10. The method according to claim 8, wherein, in the pre-lithiating, a current of 10 mA to 10 A is applied.

11. The method according to claim 8, wherein, in the pre-lithiating, current is applied for 0.1 hours to 12 hours.

12. The method according to claim 8, wherein the negative electrode current collector portion of the cutting comprises a lithium by-product layer formed through pre-lithiation reaction.

13. The method according to claim 8, wherein a process of stabilizing the metal sheet at 30° C. to 100° C. for 6 hours to 12 hours is further comprised between the pre-lithiating and the cutting.

14. The method according to claim 8, wherein, in the forming, connecting the negative electrode tabs to the negative electrode lead is performed by welding.

15. The method according to claim 14, wherein the welding is ultrasonic welding.

16. A device comprising the secondary battery according to claim 1 as a power source.

17. The device according to claim 16, wherein the device is one or more selected from a mobile phone, a portable computer, a smartphone, a smart pad, a netbook computer, a wearable device, a light electronic vehicle (LEV), a light electronic vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

[0070] FIG. 1 is graphs showing lifespan characteristics of lithium batteries according to Example 1 and Comparative Examples 1 and 2, measured in Experimental Example 2.

MODE FOR INVENTION

[0071] Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustration of the present invention and should not be construed as limiting the scope and spirit of the present invention.

Example 1

[0072] 1-1) Manufacture of Negative Electrode Plate

[0073] A negative electrode slurry, which was prepared by adding 92% by weight of a negative electrode active material including SiO and graphite in a weight ratio of 30:70, 3% by weight of Super-P as a conductive material, 3.5% by weight of SBR as a binder, and 1.5% by weight of CMC as a thickener to H.sub.2O as a solvent, was coated on a negative electrode current collector portion, except for a portion corresponding to a negative electrode tab, of a copper sheet to a thickness of 50 μm, followed by pressing. Subsequently, the negative electrode tab, which was composed of the active material-non-coated portion that was not coated with the negative electrode mixture, was coated with Al.sub.2O.sub.3 to a thickness of 0.2 μm.

[0074] This resultant copper sheet was fed into a non-aqueous EC/EMC-based electrolyte solution containing a LiCl salt and a lithium salt of 1 M LiPF.sub.6 and then a current of 100 mA was applied thereto for one hour, whereby the copper sheet was pre-lithiated as much as an irreversible amount.

[0075] Subsequently, the metal sheet was cut into the shape of a negative electrode plate including the coated negative electrode portion and the negative electrode tab.

[0076] 1-2. Manufacture of Positive Electrode Plate

[0077] Li(Ni.sub.0.8Mn.sub.0.1Co.sub.0.1)O.sub.2 was used as a positive electrode active material. 94% by weight of Li(Ni.sub.0.8Mn.sub.0.1Co.sub.0.1)O.sub.2, 3.5% by weight of Super-P as a conductive material, and 2.5% by weight of PVdF as a binder were added to NMP as a solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was coated on an aluminum foil to a thickness of 80 μm, followed by pressing and drying. As a result, a positive electrode plate was manufactured.

[0078] 1-3. Manufacture of Lithium Battery

[0079] A porous separator (Celgard™) was disposed between the manufactured positive electrode plate and negative electrode plate. Positive electrode tabs and negative electrode tabs were gathered and arranged, and then subjected to ultrasonic welding to be respectively connected to a positive electrode lead and a negative electrode lead. Subsequently, a non-aqueous EC/EMC-based electrolyte solution including containing 1 M LiPF.sub.6 was added thereto, thereby manufacturing a lithium battery.

Comparative Example 1

[0080] A lithium battery was manufactured in the same manner as in Example 1, except that an active material-non-coated portion of a negative electrode was not coated with an inorganic substance upon manufacturing of a negative electrode plate.

Comparative Example 2

[0081] A lithium battery was manufactured in the same manner as in Example 1, except that pre-lithiation reaction was not performed upon manufacture of a negative electrode plate.

Experimental Example 1

[0082] Rate characteristics of lithium secondary batteries manufactured according to Example 1 and Comparative Examples 1 and 2 were measured. To measure rate characteristics, charging/discharging was carried out at 25□ under a voltage of 2.5 V to 4.3 V. In particular, charging was performed up to 67.5 mA in a 0.1 C constant current/constant voltage (CC/CV) charging manner and discharging was performed under a cut-off condition of 2.5 V in a 0.1 C, 0.5 C, and 1 C constant current (CC) discharging manner. 0.5 C and 1 C discharge efficiencies with respect to 0.1 C discharge capacity are summarized in Table 1.

TABLE-US-00001 TABLE 1 0.1 C discharge 0.5 C discharge 2 C discharge efficiency efficiency efficiency Example 1 100% 91.2% 81.3% Comparative 100% 70.8% 37.7% Example 1 Comparative 100% 89.5% 73.9% Example 2

[0083] As shown in Table 1, it can be confirmed that the battery according to Example 1, wherein the active material-non-coated negative electrode portion was coated with the inorganic substance and pre-lithiated, exhibits superior rate performance to the battery according to Comparative Example 1, wherein the active material-non-coated negative electrode portion was not coated with the inorganic substance and was pre-lithiated.

[0084] This occurs because, when the active material-non-coated negative electrode portion is not coated with the inorganic substance, the active material-non-coated negative electrode portion is not welded with the negative electrode lead due to lithium by-products generated during pre-lithiation, or rate performance is deteriorated due to high contact resistance with the negative electrode lead.

Experimental Example 2

[0085] Lifespan characteristics of lithium secondary batteries manufactured according to Example 1 and Comparative Examples 1 and 2 were measured. So as to measure lifespan characteristics, charging was performed up to 67.5 mA at 25□ in a charging manner of constant current/constant voltage (CC/CV) of 0.5 C and 4.3 V. Discharging in a constant current (CC) discharge manner under a cut-off condition of 0.5 C and 2.5 V was performed 100 times. Results are summarized in FIG. 1.

[0086] As shown in FIG. 1, it can be confirmed that the battery of Example 1 manufactured by coating the active material-non-coated negative electrode portion with the inorganic substance and pre-lithiating exhibits superior lifespan, compared to the battery of Comparative Example 1, wherein the active material-non-coated negative electrode portion was not coated with the inorganic substance and was pre-lithiated, and the battery of Comparative Example 2, wherein the negative electrode was not pre-lithiated.

[0087] This occurs because the battery of Comparative Example 1 in which the active material-non-coated negative electrode portion was not coated with the inorganic substance, exhibits high resistance at the negative electrode lead, and decreased lifespan due to side-reaction of the lithium by-products. In addition, this occurs because, in the case of the battery of Comparative Example 2 in which the negative electrode was not pre-lithiated, Li is greatly consumed due to high irreversible capacity and great volumetric expansion, and thus, cycle lifespan is decreased.

INDUSTRIAL APPLICABILITY

[0088] Since a secondary battery according to the present invention can minimize irreversibility through pre-lithiation reaction using a high-capacity negative electrode active material, lifespan and rate characteristics thereof can be enhanced.

[0089] In addition, since an inorganic substance layer is previously formed on a negative electrode tab and then the pre-lithiation reaction is performed in a lithium-based solvent, a lithium by-product layer cannot be formed on the negative electrode tab. Accordingly, negative electrode tabs can be easily connected to a negative electrode lead, and thus, production efficiency can be enhanced.

[0090] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.